The anchor of the present invention is an improvement on the anchor device of my previously granted U.S. Pat. Nos. 3,524,228 and Reissue 27,954.
In these patents, there is disclosed an anchor for post-tensioning of prestressed concrete which includes an elongated tapering anchor case in which is movably positioned a chuck having a longitudinally tapering outer wall and comprising a plurality of wedge segments for grippingly engaging a tendon passing therethrough. In its present commercial form, the anchor case is 4.35 inches long after forming, and the chuck is 2 inches long. The anchor case includes a relatively straight, tubular, bore portion extending from the large end thereof to a point intermediate the length of the anchor case, which portion, when the anchor serves as a dead end anchor, is adapted to receive a spring and closure cap.
The angularity of the tapering anchor case bore is then altered through a substantial part of the anchor case to provide a working taper which is engaged by the outer periphery of the tapering chuck. As the tendon is jacked through the anchor, the chuck engages the tendon with progressively increased force. In order to relieve the gripping forces exerted on the tendon by the leading part of the chuck, the angularity of the anchor case taper is decreased, thereby reducing the force being exerted on the tendon at that point, with the result that the gripping force exerted by the chuck wedge segments are exerted more proportionately over a greater length of the tendon.
The anchors of the aforementioned patents further include a rolled edge at the large end of the case and a reaction plate which is engaged with the case periphery adjacent the rolled edge. A secondary reaction plate is engaged with the case periphery at a point intermediate its length and serves as a restraining element to counteract the hoop stress built up in the inside of the case by the transverse pressure of the chuck wedge segments.
In manufacture of the above anchor, the anchor case is forged, heat treated, the primary reaction plate (not heat treated) installed and the secondary reaction plate (not heat treated) installed, a total of four operations. Various sizes of this anchor are made in order to accommodate different sizes of cables such as 3/8 inch, 7/16 inch, 1/2inch, etc.